Methods for use in packaging applications using an adhesive composition

ABSTRACT

An adhesive composition and methods incorporating the adhesive composition in semiconductor applications are provided. The adhesive composition is an instant setting adhesive composition that does not require external energy input such as heat or radiation such for application of the adhesive composition on a surface. The instant setting composition possesses sufficient thixotropic characteristics such that applying the instant setting adhesive composition to a surface can be accomplished by a variety of application techniques and in a variety of patterns. Once applied to the surface, the instant setting adhesive composition sets to retain the discrete pattern as applied, in a relatively short period of time, typically from about 0.10 to about 120 seconds at an ambient temperature, typically from 20° C. to 30° C. Advantageously, the instant setting adhesive composition can be screen printed on a semiconductor wafer prior to singulation because streets between the dice are essentially free of the instant setting adhesive composition.

This is a division or application Ser. No. 09/065,944, filed Apr. 24,1998, (pending), which is a continuation-in-part of application Ser. No.08/916,629, filed Aug. 22, 1997, both of which are incorporated hereinby reference.

FIELD OF THE INVENTION

This invention relates to an adhesive composition and methods for usingan adhesive composition in die packaging applications.

BACKGROUND OF THE INVENTION

In semiconductor manufacture, a single semiconductor die (or chip) istypically mounted within a sealed package. In general, a typical packageprotects the die from damage (e.g., breakage, physical abuse, etc.) andfrom contaminants in the surrounding environment (e.g., moisture, dustparticles, etc.). In addition, the package provides a lead system forconnecting electrical devices of the die to a printed circuit board orother external circuitry.

Each die has a lower surface (also referred to as the back of the die)that is devoid of circuitry, and an upper surface (also referred to asthe face of the die) having integrated circuitry constructed thereon.The integrated circuitry is electrically accessible via die wire bondingpads which may be arranged in a variety of configurations on the face oredges of the die.

Typically, an initial component in the packaging process is a leadframe.The leadframe is a metal frame which supports several dice for packagingand provides the leads for a final semiconductor package. A typicalleadframe strip is adapted to mount several semiconductor dice.

In one a conventional packaging process, each die is attached to amounting paddle of the leadframe utilizing an adhesive layer. Theadhesive layer is typically formed from an adhesive compositionincluding an epoxy, an acrylic, a silicone or a polyimide materiallocated between the bottom surface of the die and an upper surface ofthe mounting paddle. Also, during the packaging process, bond padsformed on the die are electrically connected to the leads of theleadframe using bond wires. Following the application of a protectivelayer, for example polyimide, to the face of the die, it and a portionof the leadframe to which it is adhered is encapsulated in a polymericmaterial. Similarly, all other die-leadframe assemblies on a leadframestrip are encapsulated resulting in encapsulated interconnectedpackages, i.e., interconnected by way of the leadframe. Afterencapsulation, a trim and form operation separates the interconnectedpackages. Leads of each package are also shaped into a desiredconfiguration.

Attempts have been made to increase circuit densities and to improvepackaging technologies. For example, some high density circuits, such as16 mega bit memory devices, use lead-on-chip (LOC) packaging technology.A known lead-on-chip (LOC) semiconductor package is described in U.S.Pat. No. 4,862,245 (Pashby et al.). In general, a LOC die package isformed with a leadframe that does not include a mounting paddle formounting the die. In the LOC die package, lead fingers of the leadframeare not only for electrical attachment to the bond pads of the die viabond wires but also adhere to the face of the die and support the dieduring processing. Prior to encapsulation, the die, in effect, ismounted to the lower surface of lead fingers. This configurationprovides improved heat transfer from the die and shortens the length ofthe bond wires. In addition, this configuration enhances the reliabilityof the package seal.

One method of attaching and wire bonding a LOC die to an LOC leadframeis known as area wire bonding or A-wire bonding. When A-wire bonding isautomated, the method typically includes attaching a double-sideadhesive tape to the bottom surface of the leadframe fingers. Typically,the double-sided adhesive tape includes a thermoset adhesive on twoopposing surfaces of the tape. The face of the die is then attached to atape surface opposite the leadframe fingers. Generally, attaching theface of the die to the tape surface is accomplished in the presence ofheat and pressure. The die-tape-leadframe fingers construction is thenheated in an oven to cure the thermoset adhesive. After the adhesive iscured, the leadframe is transferred to a wirebonder machine thatconnects the bond wires to the bond pads on the die and to the leadfingers of the lead frame. Holes through the adhesive tape allow thebond wires to attach to the bond pads on the die.

In general, an A-wire process is relatively expensive and complicated.For example, the double-sided adhesive tape used in the process is anexpensive component because the tape must have an accurate configurationand must be precisely attached to the leadframe fingers for each die tobe attached. This is a delicate process and requires precise indexing ofthe die and precise alignment of the adhesive tape with the die and theleadframe fingers. Moreover, any irregularities (such as buckles,. gaps,wrinkles, etc.) in the adhesive tape during attachment to the leadframefingers tends to cause voids and adhesion problems during attachment ofthe die, which may ultimately result in the production of a defectiveproduct.

In another packaging method, a lead-under-chip (LUC) die may be attachedto leadfingers of a leadframe. For example, a tape adhesive on the backof the die or on the leadfingers, along with positioning the die on thelead fingers, results in attachment of the die to the leadframe.

Additionally, because the tape requires an accurate configurationprimarily based on the die configuration, many tape configurations(which can vary in tape width, hole patterns, etc.) are required to bestocked by semiconductor manufacturers. This also adds to the expenseand complexity of the process. Furthermore, when hole patterns arepunched out, a large amount of tape is wasted in the process.

Yet another packaging method includes attaching a semiconductor die to aleadframe as described in U.S. Pat. No. 5,286,679 (Farnworth et al.).The method includes forming a patterned layer of a thermoplastic orthermoset adhesive to one surface of a semiconductor wafer. Individualdice are then singulated from the wafer. During packaging, each adhesivecoated die is attached to lead fingers of a leadframe by heating theadhesive layer and pressing the lead fingers, adhesive and die together.This heating process is sufficient to cure the adhesive layer formedfrom a thermoplastic material. However, when the adhesive layer isformed from a thermosetting material, a separate heating step isrequired for curing.

Thus, whether adhesive tapes, thermoplastic adhesives or thermosetadhesives are used, heat, typically at a temperature of about 300° C. ormore, is generally supplied to the leadframe-adhesive-die interfaceduring packaging Which adds cost, time and equipment to the packagingprocess.

SUMMARY OF THE INVENTION

In view of the foregoing, there is a need in the semiconductor art foran improved adhesive and methods for using such an adhesive in packagingapplications. Accordingly, the present invention is directed to a methodfor forming a pattern of adhesive on a wafer, a method of attaching asemiconductor die to a leadframe, a method of making a semiconductorpackage, a semiconductor package and an adhesive composition suitablefor use in packaging applications.

One aspect of the present invention provides a method for applying anadhesive to a wafer. Preferably, the method includes the steps ofproviding a wafer having a surface; and applying an instant settingadhesive composition on the surface of the wafer in a configurationwherein a plurality of portions of the surface have the instant settingadhesive composition applied thereon, and further wherein one or morezones of the surfacet are essentially free of the instant settingadhesive composition.

The method may also include the step of singulating the wafer to form atleast one die having the instant setting adhesive composition on atleast a portion thereof. The zones may include singulation streets orregions having exposed bond pads. Additionally, the method may furtherinclude the step of applying an adhesion promoter to the surface of thewafer prior to applying the instant setting adhesive composition.

Another aspect of the present invention provides a method for applyingan adhesive to a wafer. Preferably, the method includes the steps ofproviding a wafer having a surface; and applying an instant settingadhesive composition on the surface of the wafer in a configurationwherein a plurality of portions of the surface have the instant settingadhesive composition dispensed thereon and one or more zones that areessentially free of the instant setting adhesive composition, whereinthe instant setting adhesive composition has a thixotropic index fromabout 4 to about 6. Preferably, the one or more zones includesingulation streets and regions having exposed bond pads and furthercomprising singulating the wafer along the singulation streets to format least one die having the instant setting adhesive coated on at leasta portion thereof.

According to the present invention, an instant setting adhesivecomposition is also provided. As utilized herein, the instant settingadhesive composition includes an adhesive component selected from thegroup of a cyanoacrylate adhesive, an anaerobic acrylic adhesive, andmixtures thereof; and at least one optional additive selected from thegroup of a thermal stabilizer, a thickener, a plasticizer, a toughener,a conductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent. The instant setting adhesivecomposition preferably has a thixotropic index from about 4 to about 6.Additionally, the instant setting adhesive composition preferably has athermal degradation temperature of about 300° C. or more.

In one embodiment of an instant setting adhesive according to thepresent invention, the instant setting adhesive composition includes acyanoacrylic adhesive component including a monomer of the formula:

wherein R is selected from the group of a C₁₋₆ alkyl, a cycloalkyl, analkenyl, an alkynyl, a cycloalkenyl, an alkaryl, an aralkyl, and an arylgroup. Preferably, R is selected from the group of a methyl group, anethyl group, an n-propyl group, an isopropyl group, an n-butyl group, anisobutyl group, a pentyl group, a hexyl group, an allyl group, amethallyl group, a crotyl group, a propargyl group, a cyclohexyl group,a benzyl group, a phenyl group, a cresyl group, a 2-chlorobutyl group, atrifluoroethyl group, a 2-methoxyethyl group, a 3-methoxybutyl group anda 2-ethoxyethyl group.

In another embodiment of an instant setting adhesive compositionaccording to the present invention, the instant setting adhesivecomposition includes a cyanoacrylate adhesive component comprising amonomer of the formula:

wherein R is selected from the group of a C₁₋₆ alkyl, a cycloalkyl, analkenyl, an alkynyl, a cycloalkenyl, an alkaryl, an aralkyl, and an arylgroup; and at least one optional additive selected from the group of athermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent. Preferably, the instant settingadhesive composition has a thixotropic index from about 4 to about 6.Additionally, the instant setting adhesive composition preferably has athermal degradation temperature of about 300° C. or more.

Yet another aspect of the present invention provides a method for use inpackaging a die. Preferably, the method includes the steps of providinga die; providing a leadframe; and using an instant setting adhesivecomposition to attach the one or more dice to a portion of theleadframe. Preferably, the instant setting adhesive composition includesan adhesive component selected from the group of a cyanoacrylateadhesive, an anaerobic acrylic adhesive, and mixtures thereof andfurther wherein the instant setting adhesive composition has athixotropic index from about 4 to about 6.

Preferably, the die includes the instant setting adhesive compositionapplied thereon. The instant setting adhesive composition can be appliedon a variety of portions including at least a portion of the leadframe;a back surface of the die; and at least a portion of a face surface ofthe die, which can be exposed die bond pads.

Another aspect of the present invention provides a method for use inpackaging a die. Preferably, the method includes the steps of providinga die; providing a leadframe; and using an instant setting adhesivecomposition to attach the one or more dice to a portion of the leadframeunder pressure and a temperature of about 200° C. or less.

The methods according to the present invention can further include avariety of additional steps. For example, the method can include thesteps of using an instant setting adhesive composition comprising aconductive filler to form a heat sink; and attaching the heat sink to aportion of the die or the leadframe, preferably wherein the heat sink isattached to the package. The method can also include applying anencapsulant on portions of the die attached to the leadframe, whereinthe encapsulant comprises an instant setting adhesive composition.Likewise, the method can further include using the instant settingadhesive composition comprises attaching a plurality of lead fingers ofthe leadframe to the die. Preferably, the lead fingers include theinstant setting adhesive composition applied on at least a portionthereof. The method may also further include the step of using theinstant setting adhesive composition comprises attaching the die to amounting paddle. Preferably, the mounting paddle includes the instantsetting adhesive composition applied on at least a portion thereof.

Additionally, the methods may further include the step of applying anencapsulant on portions of the die attached to the leadframe.Preferably, the encapsulant includes an instant setting adhesivecomposition. The method may also include the step of using the instantsetting adhesive composition comprises attaching a plurality of leadfingers of the leadframe to the die, wherein the lead fingers includethe instant setting adhesive composition applied on at least a portionthereof.

Yet another aspect of the present invention provides a method forattaching a semiconductor die to a leadframe. The method includesproviding an instant setting adhesive composition including an adhesivecomponent selected from the group of a cyanoacrylate adhesive, ananaerobic acrylic adhesive, and mixtures thereof and, preferably,applying the instant setting adhesive composition on at least a portionof a wafer including a plurality of dice. The method also includes thesteps of singulating dice from the wafer; and attaching a die having theinstant setting adhesive composition applied on at least a portionthereof to a portion of a leadframe. The method may also include thestep of attaching the die on a portion of the leadframe. Preferably,attaching the die on a portion of the leadframe includes positioning aportion of the die having the instant setting adhesive compositionthereon adjacent to the portion of the leadframe; and applying pressureat an elevated temperature to attach the die to the leadframe. Morepreferably, the elevated temperature is about 200° C. or less.

A further aspect of the present invention provides a method forattaching a semiconductor die to a leadframe. Preferably, die methodincludes dispensing an instant setting adhesive composition on theleadframe, wherein the instant setting adhesive composition includes anadhesive component selected from the group of a cyanoacrylate adhesive,an anaerobic acrylic adhesive, and mixtures thereof. The method alsoincludes placing the die in contact with the instant setting adhesivecomposition; and forming a bond between the die and the leadframe withthe instant setting adhesive composition. The method may also includethe additional step of applying a catalyst to the leadframe, die or tothe instant setting adhesive composition prior to forming the bondbetween the die and the leadframe. In the method, the leadframe may be amounting paddle or a lead-on-chip leadframe.

Yet a further aspect of the present invention provides a method forattaching a semiconductor die to a leadframe including the steps ofproviding the leadframe with a mounting paddle and dispensing an instantsetting adhesive composition on the mounting paddle. The method alsoincludes placing a die in contact with the instant setting adhesivecomposition; and applying pressure at a temperature of about 200° C. orless to bond the die to the leadframe with the instant setting adhesivecomposition.

Another aspect of the present invention provides a method for attachinga lead-on-chip semiconductor die to a lead-on-chip leadframe.Preferably, the method includes providing the leadframe with a pluralityof lead fingers configured to form a die mounting area and dispensing aninstant setting adhesive composition on the lead fingers in the diemounting area, said adhesive material comprising an adhesive componentselected from the group of a cyanoacrylate adhesive, an anaerobicacrylic adhesive, and mixtures thereof and an electrically insulatingfiller. The method also includes the steps of placing the die in contactwith the instant setting adhesive composition; and forming a bondbetween the die and the lead fingers with the instant setting adhesivecomposition. Preferably, the method further includes the step ofapplying a catalyst to the lead fingers, die or the instant settingadhesive composition prior to the placing step.

In the methods according to the present invention above, the dispensingstep preferably includes a method selected from the group consisting ofscreen printing, depositing and patterning, syringe applying,stenciling, dip coating, spraying, dot shooting, and combinationsthereof. Alternatively, the step of dispensing the adhesive materialincludes forming a pattern of dots.

The present invention also provides a semiconductor package includingone or more leads; a die including one or more die bond padselectrically connected to the one more leads; and an adhesive layerbetween at least a portion of the one or more leads and the die, theadhesive layer formed from an instant setting adhesive composition. Theadhesive layer can be between a back side of the die and the at leastone portion of the one or more leads or between a face side of the dieand the at least one portion of the one or more leads. Preferably, theface of the die includes at least one bond pad connected to the one ormore leads. Additionally, the semiconductor package may also include aheat sink attached to a portion of the die, wherein the heat sink isformed from an instant setting adhesive composition. The heat sink maybe attached to apportion of the package.

Another aspect of the present invention provides a semiconductor packageincluding a singulated portion of a leadframe including a mountingpaddle and a plurality of trimmed lead fingers; a die; and an instantsetting adhesive composition attaching the die to the mounting paddle.

Yet another aspect of the present invention provides a semiconductorpackage including one or more leads; a die including bond padselectrically connected to a portion of the one or more leads; and anadhesive layer between at least a portion of the one or more leads andthe semiconductor die. Preferably, the adhesive layer is formed from aninstant setting adhesive composition including a cyanoacrylic adhesivecomponent comprising a monomer of the formula:

wherein R is selected from the group of a C₁₋₆ alkyl, a cycloalkyl, analkenyl, an alkynyl, a cycloalkenyl, an alkaryl, an aralkyl, and an arylgroup; and at least one optional additive selected from the group of athermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent. Preferably, the instant settingadhesive composition has a thixotropic index from about 4 to about 6.Additionally, the instant setting adhesive composition preferably has athermal degradation temperature of about 300° C. or more.

The semiconductor packages in accordance with the present invention mayalso include an encapsulant formed from a composition comprising acomponent selected from the group of a cyanoacrylate adhesive, ananaerobic acrylate adhesive, and mixtures thereof.

These and other objects, features and advantages of the presentinvention will be apparent from the following description of variousembodiments and as illustrated in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view with parts removed from a leadframehaving a semiconductor die attached thereto in accordance with thepresent invention;

FIG. 1B is a cross sectional view taken along section line 1B—1B in FIG.1A illustrating a semiconductor package constructed in accordance withthe present invention;

FIG. 2A is a schematic plan view of a semiconductor die illustrating onepreferred applying pattern of an adhesive composition in accordance withthe present invention;

FIG. 2B is a schematic plan view of a mounting paddle of a leadframeillustrating another applying pattern of an adhesive composition inaccordance with the present invention;

FIG. 3 is a schematic block diagram of a system adapted to perform onepreferred embodiment of a method in accordance with the presentinvention;

FIG. 4 is an exploded perspective view of a LOC leadframe with an LOCdie in accordance with the present invention;

FIG. 5 is a perspective view of a packaged LOC die in accordance withthe present invention;

FIG. 6 is a plan view of a semiconductor wafer with a patterned adhesivecomposition applied thereon in accordance with the present invention;

FIG. 7 is a side elevation view taken across line C—C of thesemiconductor wafer shown in FIG. 6;

FIG. 8 is a plan view of an LOC die separated from the wafer of FIG. 6and having an adhesive composition applied in accordance with thepresent invention;

FIG. 9 is a side elevation view taken across line D—D of the die shownin FIG. 8;

FIG. 10A is an enlarged cross sectional view showing attachment of leadfingers and bond wires to an LOC die in accordance with the presentinvention;

FIG. 10B is an enlarged cross sectional view showing attachment of leadfingers and bond wires to an LUC die in accordance with the presentinvention;

FIG. 11A is a schematic view showing one preferred method for applyingan adhesive composition on a surface of a wafer or die in accordancewith the present invention;

FIG. 11B is a schematic view showing one preferred method for applyingan adhesive composition on a surface of a wafer or die in accordancewith the present invention; and

FIG. 12 is a schematic plan view showing another preferred embodiment ofthe placement of an adhesive composition on lead fingers of a leadframe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Adhesive Composition

One preferred adhesive composition comprises an instant setting adhesivecomposition. As used herein, the term “instant setting” refers to thetime required for the adhesive composition, once it is applied to asurface, become non-flowable such that the adhesive composition retainsthe discrete pattern in which it was applied. In general, the timerequired for the adhesive composition to set is about 0.10 seconds toabout 120 seconds. Preferably, the adhesive composition is instantsetting at a temperature from about 20° C. to about 30° C. and atambient atmosphere. More preferably, the time for the adhesivecomposition to become non-flowable is about 0.10 seconds to about 60seconds. Thus, an instant setting adhesive composition does not requireadditional energy input, such as heat or radiation (e.g., ultravioletlight or electron beam radiation), for application of the adhesivecomposition to a surface of a substrate. As used herein, “cure” or“cured” refers to a state of an adhesive composition wherein sufficientcrosslinking, chain extending, or both (also referred to herein as“polymerization”), has occurred such that a useful bond can no longer beformed with the adhesive composition. In contrast, and in general,thermoplastic materials are typically heated to soften the thermoplasticmaterial for application to a surface. Upon cooling to room temperature,the softened thermoplastic material typically returns to its originalcondition. Additionally, thermosetting materials are those that cureirreversibly upon heating.

An instant setting adhesive composition according to the inventionincludes an adhesive component selected from the group of acyanoacrylate adhesive; an anaerobic acrylic adhesive; and mixturesthereof. A preferred instant setting adhesive composition comprises acyanoacrylate adhesive component. In general, cyanoacrylate basedadhesive compositions are a one part system which obviates the need formetering and mixing additional components for polymerization or curingof the adhesive composition. Cyanoacrylate based adhesive compositionsgenerally do not require the presence of organic solvents whicheliminates the time, expense and potential environmental hazards posedby conventional adhesive compositions containing organic solvents thatmust be evaporated during polymerization or curing. Thus, cyanoacrylateadhesive compositions are typically substantially totally reactive.Other advantageous characteristics include high bond strength formedafter polymerization or curing and solvent resistance of the polymerizedadhesive composition.

A cyanoacrylate adhesive composition preferably includes a monomerhaving the following general formula:

wherein R is selected from the group of a C₁₋₆ alkyl, cycloalkyl,alkenyl, alkynyl, cycloalkenyl, alkaryl, aralkyl, or aryl group.Optionally, any of the above listed groups may be substituted with anon-basic group, such as oxo, halo, silicon, and ether oxygen, so longas these substitutions do not interfere with the stability and adhesionof the adhesive composition. Preferable R groups are selected from thegroup of a methyl group, an ethyl group, an n-propyl group, an isopropylgroup, an n-butyl group, an isobutyl group, a pentyl group, a hexylgroup, an allyl group, a methallyl group, a crotyl group, a propargylgroup, a cyclohexyl group, a benzyl group, a phenyl group, a cresylgroup, a 2-chlorobutyl group, a trifluoroethyl group, a 2-methoxyethylgroup, a 3-methoxybutyl group and a 2-ethoxyethyl group. Cyanoacrylateadhesives are commercially available from Loctite Corporation, RockyHill, Conn., for example, under the trade designations 410 and 416.

Another preferred instant setting adhesive composition includes ananaerobic acrylic adhesive component. An anaerobic adhesive compositionsare those that cure in the absence of oxygen, even in the absence ofoxygen in the ambient atmosphere. Typically, anaerobic adhesivecompositions cure in the presence of a metal and exposure to freeradicals. More preferred anaerobic adhesive compositions include lowmolecular weight polyfunctional methacrylates, such as described in U.S.Pat. No. 4,309,526 (Baccei).

Thixotropic Characteristic

Conventional instant setting adhesive compositions typically do notpossess sufficient thixotropic characteristics for semiconductorapplications, such as packaging assembly, particularly when thesemiconductor application is automated. Preferably, an instant settingadhesive composition in accordance with the invention has a thixotropiccharacteristic such that the adhesive composition can be dispensed in adiscrete pattern. By “discrete pattern,” it is meant that after theadhesive composition is dispensed in a desired configuration, theadhesive composition substantially maintains the configuration in whichit was applied without the need for any additional barriers or steps toprevent the borders of individual adhesive composition portions frommingling thus, rendering the configuration indeterminate. Preferably,applying the adhesive composition is accomplished by a method selectedfrom the group consisting of screen printing, depositing and patterning,syringe applying, stenciling, dip coating, spraying, dot shooting, andcombinations thereof. Alternatively, the step of dispensing the adhesivematerial includes forming a pattern of dots.

One preferred way to determine the thixotropic characteristic is by athixotropic index. As used herein, “thixotropic index” is defined as aviscosity measurement taken at a spindle speed of 0.5 rpm divided by aviscosity measurement taken at a spindle speed of 5 rpm. Viscositymeasurements are generally determined by employing a BrookfieldViscometer, for example, model HBDV-11, from Brookfield Engineering Lab,Inc., Stoughton, Ma., and a CP-51 spindle under ambient conditions(i.e., room temperature). It will be appreciated that a thixotropicindex determined for a given composition changes when viscositymeasurements are determined at different spindle speeds. Additionally,one composition cannot be directly compared to another composition whenthe thixotropic indices are determined at different spindle speeds.While not wishing to be bound by any particular theory, it is believedthat this is due, in part, to the shear conditions to which acomposition is subjected during viscosity measurement determination. Ingeneral, increasing spindle speed tends to decrease viscosity in anon-linear fashion and thus, viscosity plotted against increasingspindle speed generates a unique viscosity profile which characterizesthat composition. Preferably, an adhesive composition in accordance withthe present invention has a thixotropic index from about 4 to about 6and a viscosity of about 40,000 cps at 5 rpm.

A thixotropic index of an adhesive composition according to theinvention may be increased by the addition of a thixotropic additivethat increases the thixotropic index without altering the viscosity andadversely affecting other properties of the adhesive composition, suchas the cure time, conductivity, stability, etc. Preferably, thethixotropic additive is selected from the group of polydimethylsiloxanetreated silica, a trialkoxyalkylsilane treated silica, and mixturesthereof. The silica may either be fumed or fused silica. Examples ofcommercially available thixotropic additives includepolydimethylsiloxane treated silica, available under the tradedesignation CAB-O-SIL N70-TS, from Cabot Corporation, Boston, Mass.; andtrialkoxyalkylsilane treated silica, available under the tradedesignation AEROSIL R805, available from Degussa Corporation, RidgefieldPark, N.J.

Optional Additives

As mentioned above, conventional instant setting adhesive compositionsare typically not formulated for electronics packaging. According to thepresent invention, instant setting adhesive compositions can be modifiedto achieve the desired properties and characteristics necessary forelectronics packaging processes with various optional additives Suchoptional additives are added to improve the thermal stability,mechanical durability, electrical conductivity, dielectric strength,moisture resistivity, or other characteristics of the adhesivecomposition for a particular packaging application.

Accordingly, an adhesive composition of the present invention preferablyincludes at least one optional additive selected from the group of athermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, a colorant(e.g., a pigment or a dye), an organic solvent, and mixtures thereofRegardless of the number of optional additives included in an instantsetting adhesive composition, the total amount of the optional additivecan be about 85% by weight or less based on the total weight of theadhesive composition, depending upon the desired application for theinstant setting adhesive composition. For example, in wafer level LOCapplications, the total amount of the optional additive is about 20% byweight or less based on the total weight of the adhesive composition.

1. Thermal Stability

Preferably, an instant setting adhesive composition suitable for use insemiconductor applications has a thermal degradation temperaturesufficiently high enough so that thermal decomposition of the curedadhesive is inhibited when substrates bonded together are in use. Morepreferably, an instant setting adhesive composition has a thermaldegradation temperature of about 300° C. or more. Also preferably, aninstant setting adhesive composition has a glass transition temperatureof about 180° C. or more.

In order to increase the thermal stability of an instant settingadhesive composition, a thermal stabilizer can be added to the adhesivecomposition. Preferably, the thermal stabilizer is a compound selectedfrom the group of an alkyl 2-cyano-2,4-pentadienoate; an alkyl2-cyano-2,4-hexadienoate; an itaconic anhydride (e.g., U.S. Pat. No.3,984,749 to Konigm); a maleic anhydride (e.g., U.S. Pat. No. 3,832,334to O'Sullivan, et al.); a substituted napthasultone (e.g., U.S. Pat. No.5,424,343 to Attarwala); a di-α-cyanopentadienoate disiloxane (e.g.,U.S. Pat. No. 5,386,047 to Nakes et al.); a sulfur-containing compoundsuch as a sulfoxide, a sulfonate, a sulfinate, etc. (e.g., U.S. Pat. No.5,328,944 to Attarwala et al.),. an aromatic compound substituted withat least three electron withdrawing groups (e.g., U.S. Pat. No.5,288,794 to Attarwala); a bifunctional monomer (e.g., a (meth)acrylicacid ester, an aliphatic polyol, an aromatic polyol, to name a few); anunsaturated ester of 2-cyanoacrylic acid (e.g., U.S. Pat. No. 3,142,698to Benjamin et al., and U.S. Pat. No. 3,825,580 to Kato et al.); andmixtures thereof. Other thermal stabilizers can optionally be added toincrease the thermal degradation temperature, glass transitiontemperature or both and can be selected from the group of SiO₂, Al₂O₃,AlN, Ag, Ni, Fe, and mixtures thereof.

An instant setting adhesive composition according to the invention isalso suitable for use for attachment of heat sinks or as a heat sinkitself. In these situations, it is desirable that the instant settingadhesive composition, a particularly preferred thermally conductivefiller is silica coated aluminum nitride such as that commerciallyavailable under the trade designation SCAN, from Dow Chemical, MidlandMich., and boron nitride, which is readily commercially available from avariety of sources.

2. Mechanical Durability

Mechanical durability of an instant setting adhesive composition may beimproved by including a thickener, a plasticizer, and a toughener in aninstant setting adhesive composition according to the invention. Athickener may be added to increase viscosity of an instant settingadhesive composition. For example, a thickener is particularly desirableto include in an instant setting adhesive composition including acyanoacrylate adhesive component because this type of adhesivecomposition typically has a viscosity of only about 10 to about 100centipoises. However, a higher thixotropic index and a higher viscosityare desired for certain dispensing techniques, such as screen printing.Preferred thickeners are polymeric additives including, but not limitedto, poly(methyl) methacrylate, methacrylate-type copolymers, acrylicrubbers, cellulose derivatives, polyvinyl acetate, andpoly(α-cyanoacrylate).

A plasticizer may be added to an instant setting adhesive composition inaccordance with the present invention. The addition of a plasticizer ispreferably included when it is desired to improve the agingcharacteristics of the adhesive composition after it is cured todecrease the brittleness. A plasticizer is preferably selected from thegroup of monofunctional and difunctional aliphatic esters of acidscontaining from 1 to about 10 carbon atoms. Examples of suchplasticizers include dimethyl octyl sebacate and esters of malonic acid,difunctional aromatic esters, phosphates and phosphonates.

A toughener may also be added to an adhesive composition. Typically,tougheners are polymeric additives and, are more preferably, selectedfrom the group of acrylic elastomers, acrylonitrile copolymerelastomers, fluoro elastomers, and mixtures thereof. If used insufficient amount, these polymeric additives may also serve as athickener.

Mechanical strength may also be improved by including SiO₂ and SiC in aninstant setting adhesive composition of the invention.

3. Electrical Conductivity

Electrical conductivity may be improved by including a conductive fillerin an instant setting adhesive composition according to the invention.Examples of conductive fillers include Ag, Ni, and Pd. An electricallyconductive filled instant setting adhesive composition is typicallyrequired for applications such as for interconnect device backsideconductivity or for wire bond monitoring system (WBMS).

4. Dielectric Property

Because an instant setting adhesive composition according to theinvention is suitable for attachment of a die to a leadframe, forexample, it is desirable that the instant setting adhesive compositionpossess a dielectric constant of about 4 or less. Additionally, aninstant setting adhesive composition is also suitable for use as anencapsulant. Dielectric strength may be increased by including SiO₂ orfluorinated polyimide in an instant setting adhesive compositionaccording to the invention.

5. Moisture Resistivity

When desirable, a moisture stabilizer may be added to an instant settingadhesive composition according to the invention to improve adhesionfunction in increased humidity. This is particularly desirable when theambient atmosphere has a high moisture content because instant settingadhesive compositions including a cyanoacrylate adhesive component tendto easily cure anionically in the presence of trace amounts of moisture.One preferred moisture stabilizer that can be added to an instantsetting adhesive composition is an ester, wherein an alcohol residue ofthe ester contains a dipentaerythritol residue and an acid residue ofthe ester is an acrylic acid residue or a methacrylic acid residue, forexample, as described in U.S. Pat. No. 5,536,799 (Takahashi et al.).Another preferred moisture stabilizer that can be added to an instantcure adhesive composition is a monomeric fluorinated ether ofdimethylvinylethynylcarbinol, such as that described in U.S. Pat. No.4,167,546 (Korshak, et al.).

6. Adhesive Stabilization

Other characteristics that may be altered are the adhesion of thesubstrates and the rate of cure. Thus, optional additives can furtherinclude an adhesion promoter and a storage stabilizer.

An adhesion promoter can either be added to an instant setting adhesivecomposition according to the invention or it can be applied to thesurface of the substrate to be adhered prior to the application of theinstant setting adhesive composition. For example, an adhesion promotercan be applied a surface of the die 10 or a surface of the mountingpaddles 12 to accelerate curing of the adhesive layer 20 (FIG. 1B).Suitable adhesion promoters include deionized (DI) water;3,4,5-trihydroxybenzoic acid and esters thereof (e.g., U.S. Pat. No.4,139,693 to Schoenberg); and a quaternary ammonium compound havingnitrogen bonded pendant C₁-C₂₂ alkyl or hydroxyalkyl groups, such asthose described in U.S. Pat. No. 5,079,098 (Liu).

Storage (or adhesive) stabilizers may also be used to stoppolymerization at a desired thickness, at a gap between the bondedsurfaces, or during storage of bulk instant setting adhesivecompositions. Suitable adhesive stabilizers are generally either anionicpolymerization inhibitors or free radical inhibitors. Suitable anionicpolymerization inhibitors typically have a pK_(a) of about 4 or less andare usually acids, or anhydrides thereof. Examples of useful anionicpolymerization inhibitors include sulfur dioxide, nitric acid, hydrogenfluoride, hydrochloric acid, sulfuric acid, phosphoric acid, sulfonicacid, carboxylic acid, acetic acid, carboxylic acid anhydrides,phosphoric acid anhydrides, sultones, acid chlorides, and the like.

Suitable free radical inhibitors include phenolic compounds such asquinone, hydroquinone, t-butyl catechol, p-methoxyl-penol, and the like.

7. Other Optional Additives

Other optional additives that may be included in the adhesivecomposition of the present invention include a colorant (e.g., a pigmentor a dye) as is known in the art.

Packaging Applications

Referring to FIGS. 1-2, packaging using a leadframe having mountingpaddles is described. In this packaging method, an instant settingadhesive composition is applied in-line, as described below. Asemiconductor die 10 is shown attached to a leadframe 14 in accordancewith the present invention. As previously described, the leadframe istypically adapted to mount a plurality of dice. A semiconductor die 10includes a pattern of bond pads 18 in electrical communication with theintegrated circuits of the die 10. The leadframe 14 comprises aconventionally formed metal leadframe having mounting paddles 12 andpaddle support bars 13. In addition, the leadframe 14 includes anarrangement of lead fingers 16. Wires 15 are bonded to the bond pads 18on the die 10 and to bonding sites on the lead fingers 16 to formseparate electrical paths therebetween.

FIG. 1B illustrates a semiconductor package 17 after singulation fromthe leadframe 14. As shown in FIG. 1B, the package 17 includes the die10, which has been attached to the mounting paddle 12 using a curedadhesive layer 20. Further details of the attachment process will behereinafter described. The semiconductor package 17 also includes aplastic encapsulant 19 which encapsulates the die 10 and portions of thelead fingers 16A. Leads 16A for the package 17 comprise trimmed andformed portions of the lead fingers 16 (FIG. 1A). Additionally, thesemiconductor package 17 may include a heat sink for dissipating heatgenerated in the device during operation. A heat sink 31 a may beincluded within the encapsulant 19 in close proximity to the die 10.Alternatively, a heat sink 31 b may be included, on a surface of theencapsulant 19.

Preferably, the method of the invention is practiced using an instantsetting adhesive composition including an adhesive component selectedfrom the group of a cyanoacrylate adhesive, an anaerobic acrylicadhesive, and mixtures thereof, as described above. The adhesivecomposition can be applied by any suitable in-line applying mechanismincluding screen printing, syringe applying, stenciling, dip coating,spraying, and dot shooting mechanisms. A total volume of the adhesivecomposition applied to the leadframe 12 (or to the die 10) is dependenton the size of the die 10 and a desired thickness of the adhesive layer20 (FIG. 1B). A representative total volume of adhesive composition fora 4.4 mm×9.4 mm die is preferably from about 0.0025 grams to about0.0011 grams. The resultant adhesive layer 20 (FIG. 1B) preferably has athickness from about 0.25 mils to about 2 mils.

Preferably, immediately subsequent to applying the instant settingadhesive composition on the mounting paddles 12 (or alternately on thedie 10), the die 10 can be placed in contact with the adhesivecomposition. The applying and placing steps can be performed using asystem 22, which is shown schematically in FIG. 3. This illustrativesystem 22 can include components of a conventional die attach machineconfigured for polymer bonding of die to leadframes. One suitable dieattach machine is manufactured by ESC Manufacturing Company of Ivy Land,Pa., and is designated a Model No. 9200. It will be recognized by oneskilled in the art that alternate system configurations may be used tocarry out the processes described herein.

The system 22 can include a leadframe feed mechanism 42 for manipulatingthe leadframes 14, and a vacuum tool 44 for manipulating the die 10. Inaddition, the system 22 can include a applying mechanism 46 for applyinga desired volume of instant setting adhesive composition to the mountingpaddles 12 (FIG. 1A) of the leadframes 14.

The system 22 can also include an optical alignment device 48 foraligning the die 10 to the mounting paddles 12. Still further, thesystem 22 can include a die support platform 50 for placing the die 10in contact with the mounting paddles 12 with a required pressure.Preferably, this pressure can be in the range of 75 to 100 gm/die. Thepressure is generally applied in conjunction with heat. According to thepresent invention, a bonding temperature is preferably about 200° C. orless. This bonding temperature is somewhat less that what is appliedwhen conventional thermoplastic adhesive compositions are used.Conventional thermoplastic adhesive compositions typically utilize abonding temperature of about 300° C. or more.

Curing or polymerizing the instant setting adhesive compositioninitiates when the die 10 is placed in contact with the instant settingadhesive composition on the mounting paddles 12. With the adhesivesandwiched between the die 10 and mounting paddles 12, a small amount ofmoisture contained on the mounting paddles 12 at the bonding temperatureis generally sufficient to initiate anionic polymerization of theinstant setting adhesive to form the cured adhesive layer 20 (FIG. 1B).Curing of the instant setting adhesive composition is preferablycompleted in a period of time from about 1 second or less. In thismanner, the semiconductor die 10 can be bonded to leadframe 14 withoutheating the die 10 or leadframe 14. The adhesive layer 20 (FIG. 1B)formed in this manner is sufficiently strong to withstand conditions towhich die will be exposed to during use in electronic equipment.

Additionally, an instant setting adhesive composition of the presentinvention may be used to attach the heat sink 31 a or 31b or it may formthe heat sink itself. In either instance, it is preferable that theinstant setting adhesive composition possess suitable thermal stabilitycharacteristics, as described above. The system 22 (FIG. 3) may includea mechanism for applying the instant setting adhesive composition priorto application of the heat sink or to form the heat sink, as desired.

Referring to FIGS. 4 and 5, another packaging application using aninstant setting adhesive composition applied in-line is described. Alead-on-chip (LOC) die 110 and a lead-on-chip (LOC) leadframe 112 areshown. The LOC die 110 is thin, flat, and generally rectangular in shapeand includes a die face 114, or active side, wherein the integratedcircuitry is formed. A plurality of die wire bonding pads 116 are formedacross the center and side edges of the die 110 in electrical contactwith the integrated circuitry of the die 110.

The leadframe 112 is formed from metal sheet and includes side rails118, 120 formed with indexing holes 122. The indexing holes 122facilitate transport and indexing of the leadframe 112 by automatedpackaging machinery. The leadframe 112 also includes sidebars 124, 126(or dambars) for increased rigidity and to limit the flow ofencapsulating material during the encapsulation process. The side rails118, 120 and sidebars 124, 126 are trimmed away during a trim and formoperation.

Furthermore, the leadframe 112 includes a plurality of generallyparallel and spaced lead fingers 128. During the packaging process, thedie 110 is attached to at least a portion of the lead fingers 128.Attachment is accomplished using an instant setting adhesive compositionas described herein. The instant setting adhesive composition may beapplied to portions of the leadfingers 128 or to portions of a face ofthe die 110 resulting in a cured layer between the portions of the die110 and portions of the lead fingers 128.

The lead fingers 128 are connected to thin bond wires 130 (FIG. 5),which also connect to the wire bond pads 116. The lead fingers 128 thusfunction to electrically connect the integrated circuitry of the LOC die110 to external circuitry (e.g., a printed circuit board). In addition,the lead fingers 128 function to support the LOC die 110 during thepackaging process and to facilitate heat transfer from the LOC die 110.The leadframe 112 also includes bus bars 132 for making multipleconnections to the wire bond pads 116.

Referring to FIG. 5, the packaged LOC die 110 or semiconductor package(or module) 134 is shown. The semiconductor package 134 includes anencapsulating material 136 which encapsulates the chip 110 and all but aterminal portion 138 of the lead fingers 128. Kinks 140 in the leadfingers 128 help to strengthen the assembly. The encapsulating material136 may be formed from an instant setting adhesive composition, asdescribed above. The LOC die 110 is located in the center of the package134 with the wire bond pads 116 of the die 110 connected to the thinbond wires 130, which in turn connect to the lead fingers 128. Portionsof the lead fingers 128 are attached to the front side 114 of the die110, or to an alpha barrier (not shown) attached to the die 110 using aninstant setting adhesive composition. Prior to encapsulation, the leadfingers 128 provide the only physical connection between the leadframe112 and the LOC die 110. In a lead-under-chip (LUC) device, packagingmay be accomplished by applying an instant setting adhesive compositionin-line to at least portions of a back side of the die or to portions ofthe lead fingers to which the die is attached.

Referring now to FIGS. 6-12, a semiconductor wafer 142 including aninstant setting adhesive composition 146 dispensed thereon and packagesresulting therefrom, in accordance with the invention are described. Thewafer 142 is manufactured for producing a plurality of dice 144 usingvarious techniques which are known in the art. In accordance with themethod of the invention, a first side of the wafer 142, shown as a frontside 150 of the wafer 142, is coated with an instant setting adhesivecomposition 146. Deposition of the adhesive composition 146 may, forexample, follow the deposition of a final insulating/passivating layeron the wafer 142. Alternately, as shown in FIG. 10B, the back side 151of the wafer 142 may also be coated with an instant setting adhesivecomposition 146 for lead-under-chip (LUC) die bonding, conventional diebonding, or as an adhesive interface for chip stacking.

The present invention includes applying an instant setting adhesivecomposition on at least a portion of a wafer, singulating dice from thewafer, and attaching a die to at least a portion of a leadframe.Further, the instant setting adhesive composition is applied on a firstsurface of a semiconductor wafer in a configuration wherein a pluralityof portions having the instant setting adhesive composition dispensedthereon are separated by zones that are essentially free of the instantsetting adhesive composition. The first surface of the wafer on whichthe instant setting adhesive composition is dispensed can be a frontside of the wafer for attaching lead-on-chip (LOC) dice to a leadframe,or it can be a back side of the wafer for attaching lead-under-chip(LUC) dice to a leadframe (or a mounting paddle) or for chip stacking.

An instant setting composition 146 is preferably dispensed on the wafer142 (and die 144) with a thickness of between about 8 μm to about 200μm. The instant setting adhesive composition 146 may be applied to thewafer 142 in a pattern by any suitable deposition method. Preferableapplication methods are selected from the group of screen printing,deposition and patterning, syringe applying, stenciling, dip coating,spraying, dot shooting, and combinations thereof.

One preferred method is a screen printing process. A screen printingprocess is similar to a silk screening process used for printingT-shirts and artwork. Such a process is shown schematically in FIG. 11A.With a screen printing process, the wafer 142 is coated with an instantsetting adhesive composition 146 dispensed from a nozzle 172. Apatterned screen 166 is situated between the wafer 142 and the nozzle172 to provide the desired pattern. In addition, a dockering roller 168(or blade), movably mounted for motion across the screen 166, asindicated by arrow 170, can be used to aid in the distribution of theadhesive.

Another preferred method is a stenciling process. A stenciling processis shown schematically in FIG. 11B. In a stenciling process, a stencil167 is placed over the desired surface to be coated with the instantsetting adhesive composition. The stencil 167 is typically a rigidstructure having a pattern therein and can be formed from a variety ofconventional materials that do not chemically react with screen printingpaste. The pattern included in the stencil 167 includes a plurality ofapertures 177 separated by solid portions (not labeled) of the stencil,wherein the plurality of apertures correspond to the desired locationfor dispensing the instant setting adhesive composition on the die 144.A quantit) of the instant setting adhesive composition 146′ is dispensedon a solid portion of the stencil 167, although the exact amount of theinstant setting adhesive composition is not critical. A flexible blade175 is positioned near the quantity of the instant setting adhesivecomposition 146′. The flexible blade 175 moves in one direction, shownfor example as arrow A so as to pull the quantity of the instant settingadhesive composition against the stencil. Thus, it is similar inoperation to that of a squeegee. As the flexible blade 175 is drawn overthe surface of the stencil 167, a portion of the instant settingadhesive composition 146′ falls through the plurality of apertures 177to form a layer of instant setting adhesive composition 146 in thediscrete pattern corresponding to the plurality of apertures 177 in thestencil 167. Accordingly, because the instant setting adhesivecomposition can be applied at room temperature and sets to form adiscrete pattern, stenciling is an advantageous method of applicationbecause special heating equipment is not required to apply the instantsetting adhesive composition.

Furthermore, an instant setting adhesive composition could be depositedand patterned using a resist pattern with a solvent. This is sometimesreferred to as a resist etch back. In general, such a resist etch backwould involve patterning the adhesive composition with a patternedresist layer and then removing the resist with a suitable solvent,leaving the patterned instant setting adhesive composition.

Following or during the adhesive deposition process, the adhesivecomposition 146 is patterned such that streets (or zones) 152 are formedbetween the individual dice 144, such as by the methods described above.This is particularly useful for singulating the dice 144, e.g. sawcutting the dice. Preferably, these zones 152 are substantially free ofadhesive 146, as shown in FIGS. 6 and 7. These streets 152 are alsovariously known in the art as scribe lines, saw lines, or avenues. Withthe streets 152 free of adhesive, the efficiency of the saw cuttingprocedure is unaffected by the adhesive layer 146. It is to beunderstood, however, that the invention can be practiced with adhesivelocated in the streets 152.

With respect to LOC packaging processes as shown at least in part inFIGS. 8-10A, in addition to the streets 152 preferably being essentiallyfree of adhesive, the adhesive layer 146 is patterned such that the bondpads 154 (FIG. 8) for the dice 144 are also free of adhesive. As shownin FIG. 8, this may be accomplished by patterning a substantiallyadhesive free area 156 around the bond pads 154. This may also beaccomplished by a finer patterning of the adhesive layer 146 such thatrather than having wide adhesive free areas, only the bond pads 154 areclear of adhesive (not shown).

With each die 144 coated with an instant setting adhesive composition146, as shown in FIGS. 8 and 9, the lead fingers 158, 160 of a leadframecan be attached to the die 144 by the application of heat and pressure,as indicated by pressure arrow 180, 182, in FIG. 10A. Pressure may beapplied by a suitable technique such as a movable arm pressing theassembly against a stationary platen. Under the effect of heat andpressure, the adhesive composition 146 is in effect sandwiched betweenthe lead fingers 158, 160 and the die 144 to form an adhesive bond orlayer therebetween. This firmly attaches the die 144 to the lead fingers158, 160 for the subsequent encapsulation process.

As shown in FIG. 10B, the die 144 includes bond pads 154 on one surface(typically the face surface). A back surface 151 is attached to leadfingers 158 with an instant setting adhesive composition 146. Asdescribed with respect to FIG. 10A, the lead fingers 158, 160 of aleadframe can be attached to the back surface 151 of the die 144 by theapplication of heat and pressure, as indicated by pressure arrow 180,182. Again, under the effect of heat and pressure, the adhesivecomposition 146 is sandwiched between the lead fingers 159, 160 and theback surface 151 of the die 144 to form an adhesive bond or layertherebetween. This firmly attaches the die 144 to the lead fingers 158,160 for the subsequent encapsulation process.

In forming a bond between any of the substrates described above with theinstant setting adhesive composition as described herein, the pressurethat is applied is typically about 5 kg of applied force. Heat is alsoapplied at a temperature of about 200° C. or less. Typically, a bondforms in about 1 second or less.

Following attachment of the die 144 and lead fingers 158, 160, fine bondwires 162, 164 can then be attached to the bond pads 154 of the die 144and to the lead fingers 158, 160 during a wire bonding process.Additionally, any other electrical connecting processes may be used forconnection of bond pads to lead fingers. For example, TAB bonding may beused as opposed to wire bonding.

After wire bonding, an encapsulation process is performed to completethe semiconductor package. An instant setting adhesive may be used toencapsulate the die. The result is a package substantially similar tothe package described with reference to FIGS. 4-5. Further, a step ofattaching a heat sink (not shown) can be included in a method inaccordance with the invention, such as described with reference to FIG.1B. In one embodiment, attaching a heat sink generally includes applyingan instant setting adhesive composition on at least one surface of thedie either prior to or after singulation from the wafer and attaching aheat sink thereto. In an alternative embodiment, attaching a heat sinkgenerally includes applying an instant setting adhesive composition onat least one surface of the packaged die or encapsulated package, i.e.,the instant setting adhesive composition functions as the heat sink. Ineither embodiment, the instant setting adhesive composition is thermallyconductive. In these applications, the instant setting adhesivecomposition preferably contains a conductive filler, more preferably athermally conductive filler, as described above. The heat sinkdissipates heat generated when the electronic package is in operation.

In addition to forming an adhesive layer 147 for attaching the die 144to the lead fingers 158, 160 or a leadframe, an instant setting adhesivecomposition 146 can also be formulated to function as an additionalpassivating/insulating layer for the wafer 142 and the die 144. As anexample, the instant setting adhesive composition 146 may he formulatedto provide complete coverage of the die 144 similar to a die coat forBTMS (bottom to top metal shorts and thin film crack) protection. Theinstant setting adhesive composition 146 may also be formulated in someapplications to function as an alpha barrier. In general, alpha barrierspreferably have a melting temperature in excess of 175° C. and do notcontain ionizable species such as halides and active metals.

In a further packaging process, an instant setting adhesive composition174 is applied directly to the lead fingers 176 of a leadframe 178instead of to the front side of the wafer or die, as previouslydescribed. The adhesive composition 174 may be deposited in a patternthat matches the placement of the lead fingers on the die (e.g., justthe ends of the lead fingers 176). As an example, the adhesivecomposition 174 can be dispensed on the lead fingers 176 using a sprayon applying system similar to the screen printing process shown in FIG.12. In addition, an electrostatic charge can be utilized to aid in thedistribution of the adhesive composition on the lead fingers 176. Thiscan be accomplished by charging an instant setting adhesive compositionand influencing its deposition pattern on the lead fingers 174 usingsuitably located charge plates.

Further applications will be recognized by those with skill in the art.For example, an instant setting adhesive composition may be used inleadless chip carriers, surface mount carriers, and chip on boardmodules.

EXAMPLE 1

An instant setting adhesive composition including a cyanoacrylateadhesive monomer commercially available from Loctite Corporation, RockyHill, Conn., under the trade designation “416,” was applied as a patternof dots to the mounting paddle of a copper leadframe. A total volume ofthe adhesive monomer was about 0.005 grams. A semiconductor die having a3 mm×5.6 mm footprint was manually positioned upon the mounting paddle.Curing occurred within about 10 seconds to form an adhesive layer about0.2 mils thick. The adhesion force of the resulting bond was measured tobe about 1.7 kg. Application and curing of the adhesive was performed ata room temperature of between about 20° C. to 30° C.

EXAMPLE 2

A plurality of semiconductor die having a footprint of 3 mm×5.6 mm weresecured to separate mounting paddles of a copper alloy leadframe using aModel No. 9200 die attacher from ESC Manufacturing Company, Warrington,Pa. Different cyanoacrylate adhesive monomers sold by LoctiteCorporation, Rocky Hill, Conn., under the trade designations “410” and“416,” were applied and cured at a room temperature of from 20° C. to30° C. A total volume of adhesive was about 0.005 grams applied invarious dot patterns to form adhesive layers about 0.2 mils thick. Bothadhesives were found to cure in seconds with a bonding force of about1.7 kg/die.

All patents, patent documents, and publications cited herein areincorporated by reference as if each were individually incorporated byreference. Various modifications and alterations of this invention willbe apparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not limited to the illustrative embodiments set forthherein.

What is claimed is:
 1. A method for applying an adhesive to a wafercomprising: providing a wafer having a surface; and applying an instantsetting adhesive composition on the surface of the wafer in aconfiguration wherein a plurality of portions of the surface have theinstant setting adhesive composition applied thereon, and furtherwherein one or more zones of the surface are essentially free of theinstant setting adhesive compositio, wherein the instant settingadhesive composition comprises: an adhesive component selected from thegroup of a cyanoacrylate adhesive, an anaerobic acrylic adhesive, andmixtures thereof, wherein the adhesive component comprises a monomer ofthe formula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about
 6. 2. Themethod of claim 1 further comprising singulating the wafer to form atleast one die having the instant setting adhesive composition on atleast a portion thereof.
 3. The method of claim 2 wherein the zonescomprise singulation streets.
 4. The method of claim 1 wherein the zonescomprise regions having exposed bond pads.
 5. The method of claim 1wherein applying the instant setting adhesive composition to the surfaceof the wafer comprises a technique selected from the group of screenprinting, depositing and patterning, syringe applying, stenciling, dipcoating, spraying, dot shooting, and combinations thereof.
 6. The methodof claim 1 further comprising applying an adhesion promoter to thesurface of the wafer prior to applying the instant setting adhesivecomposition.
 7. The method of claim 1 wherein R is selected from thegroup of a benzyl group and a cresyl group.
 8. A method for applying anadhesive to a wafer comprising: providing a wafer having a surface; andapplying an instant setting adhesive composition on the surface of thewafer in a configuration wherein a plurality of portions of the surfacehave the instant setting adhesive composition dispensed thereon and oneor more zones are essentially free of the instant setting adhesivecomposition, wherein the instant setting adhesive composition has athixotropic index from about 4 to about 6, and becomes non-flowable andsubstantially maintains the configuration in which the instant settingadhesive composition was applied within about 0.1 seconds to about 120seconds at a temperature of about 20° C. to about 30° C. after theinstant setting adhesive composition is applied to the surface.
 9. Themethod of claim 8 wherein applying the instant setting adhesivecomposition comprises one of stenciling and screen printing.
 10. Themethod of claim 8 wherein the instant setting adhesive comprises anadhesive component selected from the group of a cyanoacrylate adhesive,an anaerobic acrylic adhesive, and mixtures thereof.
 11. The method ofclaim 8 wherein the one or more zones include singulation streets andregions having exposed bond pads and further comprising singulating thewafer along the singulation streets to form at least one die having theinstant setting adhesive coated on at least a portion thereof.
 12. Themethod of claim 8 wherein the instant setting adhesive compositionbecomes non-flowable and substantially maintains the configurationwithin about 0.1 seconds to about 60 seconds.
 13. A method for use inpackaging a die comprising: providing a die; providing a leadframe; andusing an instant setting adhesive composition to attach the die to aportion of the leadframe, wherein the instant setting adhesivecomposition comprises: an adhesive component selected from the group ofa cyanoacrylate adhesive, an anaerobic acrylic adhesive, and mixturesthereof, wherein the adhesive component comprises a monomer of theformula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about
 6. 14. Themethod of claim 13 wherein the die includes the instant setting adhesivecomposition applied thereon.
 15. The method of claim 13 wherein theleadframe includes the instant setting adhesive composition applied onat least a portion thereof.
 16. The method of claim 15 wherein the dieincludes the instant setting adhesive composition applied on a backsurface of the die.
 17. The method of claim 16 wherein the die includesthe instant setting adhesive composition applied on at least a portionof a face surface of the die.
 18. The method of claim 17 wherein theface surface of the die comprises exposed die bond pads.
 19. The methodof claim 13 further comprising using an instant setting adhesivecomposition comprising a conductive filler to form a heat sink; andattaching the heat sink to a portion of the die or the leadframe. 20.The method of claim 19 wherein the method further comprises assembling apackage including the die and the leadframe, wherein the heat sink isattached to the package.
 21. The method of claim 13 wherein using theinstant setting adhesive composition comprises attaching a plurality oflead fingers of the leadframe to the die, wherein the lead fingersinclude the instant setting adhesive composition applied on at least aportion thereof.
 22. The method of claim 13 wherein using the instantsetting adhesive composition comprises attaching the die to a mountingpaddle, wherein the mounting paddle includes the instant settingadhesive composition applied on at least a portion thereof.
 23. Themethod of claim 13 wherein using the instant setting adhesivecomposition comprises using a technique selected from the group ofscreen printing, depositing and patterning, syringe applying,stenciling, dip coating, spraying, dot shooting, and combinationsthereof to apply the instant setting adhesive composition.
 24. A methodfor use in packaging a die comprising: providing a die; providing aleadframe; using an instant setting adhesive composition to attach thedie to a portion of the leadframe, wherein the instant setting adhesivecomposition comprises an adhesive component selected from the group of acyanoacrylate adhesive, an anaerobic acrylic adhesive, and mixturesthereof and further wherein the instant setting adhesive composition hasa thixotropic index from about 4 to about 6; and applying an encapsulanton portions of the die attached to the leadframe, wherein theencapsulant comprises an instant setting adhesive composition.
 25. Amethod for use in packaging a die comprising: providing a die; providinga leadframe; and using an instant setting adhesive composition to attachthe die to a portion of the leadframe under pressure and a temperatureof about 200° C. or less, wherein the instant setting adhesivecomposition comprises: an adhesive component selected from the group ofa cyanoacrylate adhesive, an anaerobic acrylic adhesive, and mixturesthereof, wherein the adhesive component comprises a monomer of theformula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about
 6. 26. Themethod of claim 25 wherein the die includes the instant setting adhesivecomposition applied thereon.
 27. The method of claim 25 wherein theleadframe includes the instant setting adhesive composition applied onat least a portion thereof.
 28. The method of claim 27 wherein the dieincludes the instant setting adhesive composition applied on a backsurface of the die.
 29. The method of claim 25 wherein the die includesthe instant setting adhesive composition applied on at least a portionof a face surface of the die.
 30. The method of claim 29 wherein theface surface of the die comprises exposed die bond pads.
 31. The methodof claim 25 further comprising using an instant setting adhesivecomposition comprising a conductive filler to form a heat sink; andattaching the heat sink to a portion of the die or the leadframe. 32.The method of claim 31 wherein the method further comprises assembling apackage including the die and the leadframe, wherein the heat sink isattached to the package.
 33. The method of claim 25 wherein using theinstant setting adhesive composition comprises attaching a plurality oflead fingers of the leadframe to the die, wherein the lead fingersinclude the instant setting adhesive composition applied on at least aportion thereof.
 34. The method of claim 25 wherein using the instantsetting adhesive composition comprises attaching the die to a mountingpaddle, wherein the mounting paddle includes the instant settingadhesive composition applied on at least a portion thereof.
 35. Themethod of claim 25 wherein using the instant setting adhesivecomposition comprise using a technique selected from the group of screenprinting, depositing and patterning, syringe applying, stenciling, dipcoating, spraying, dot shooting, and combinations thereof to apply theinstant setting adhesive composition.
 36. A method for use in packaginga die comprising: providing a die; providing a leadframe; using instantsetting adhesive composition to attach the die to a portion of theleadframe under pressure and a temperature of about 200° C. or less; andapplying an encapsulant on portions of the die attached to theleadframe, wherein the encapsulant comprises an instant setting adhesivecomposition.
 37. A method for attaching a semiconductor die to aleadframe comprising: providing an instant setting adhesive composition;applying the instant setting adhesive composition on at least a portionof a wafer including a plurality of dice; and singulating dice from thewafer; and attaching a die having the instant setting adhesivecomposition applied on at least a portion thereof to a portion of aleadframe, wherein the instant setting adhesive composition comprises:an adhesive component selected from the group of a cyanoacrylateadhesive, an anaerobic acrylic adhesive, and mixtures thereof, whereinthe adhesive component comprises a monomer of the formula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, a colorantand an organic solvent; wherein the instant setting adhesive compositionhas a thixotropic index from about 4 to about
 6. 38. The method of claim37 wherein the portion of the leadframe comprises a mounting paddle andthe surface of the wafer comprises a back surface of the wafer.
 39. Themethod of claim 37 wherein applying the instant setting adhesivecomposition comprises applying the instant setting adhesive compositionin a pattern on the wafer, the pattern including the instant settingadhesive composition on regions of the wafer such that singulationstreets and bond pads being essentially free of the instant settingadhesive composition.
 40. The method of claim 37 wherein attaching thedie on a portion of the leadframe comprises: positioning a portion ofthe die having the instant setting adhesive composition thereon adjacentto the portion of the leadframe; and applying pressure at an elevatedtemperature to attach the die to the leadframe.
 41. The method of claim40 wherein the elevated temperature is about 200° C. or less.
 42. Themethod of claim 37 wherein the portion of the leadframe comprises one ormore lead fingers of a lead on chip leadframe and the surface of thewafer comprises a face surface of the wafer.
 43. The method of claim 37wherein the portion of the leadframe comprises one or more lead fingersand the surface of the wafer comprises a back surface of the wafer. 44.A method for attaching a semiconductor die to a leadframe comprising:dispensing an instant setting adhesive composition on the leadframe;placing the die in contact with the instant setting adhesivecomposition; and forming a bond between the die and the leadframe withthe instant setting adhesive composition, wherein the instant settingadhesive composition comprises: an adhesive component selected from thegroup of a cyanoacrylate adhesive, an anaerobic acrylic adhesive, andmixtures thereof, wherein the adhesive component comprises a monomer ofthe formula:

 wherein R is selected from group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyhexyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about
 6. 45. Themethod of claim 44 further comprising applying a catalyst to theleadframe, die or to the instant setting adhesive composition prior toforming the bond between the die and the leadframe.
 46. The method ofclaim 44 wherein the leadframe includes a mounting paddle.
 47. Themethod of claim 44 wherein the leadframe comprises a lead-on-chipleadframe.
 48. A method for attaching a semiconductor die to a leadframecomprising: providing the leadframe with a mounting paddle; dispensingan instant setting adhesive composition on the mounting paddle; placinga die in contact with the instant setting adhesive composition; andapplying pressure at a temperature of about 200° C. or less to bond thedie to the leadframe with the instant setting adhesive composition,wherein the instant setting adhesive composition comprises: an adhesivecomponent selected from the group of a cyanoacrylate adhesive, ananaerobic acrylic adhesive, and mixtures thereof, wherein the adhesivecomponent comprises a monomer of the formula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about
 6. 49. Themethod of claim 48 wherein dispensing the instant setting adhesivecomposition comprises a method selected from the group consisting ofscreen printing, depositing and patterning, syringe applying,stenciling, dip coating, spraying, dot shooting, and combinationsthereof.
 50. The method of claim 48 wherein dispensing the instantsetting adhesive composition comprises forming a pattern of dots.
 51. Amethod for attaching a lead-on-chip semiconductor die to a lead-on-chipleadframe comprising: providing the leadframe with a plurality of leadfingers configured to form a die mounting area; dispensing an instantsetting adhesive composition on the lead fingers in the die mountingarea; placing the die in contact with the instant setting adhesivecomposition; and forming a bond between the die and the lead fingerswith the instant setting adhesive composition, wherein the instantsetting adhesive composition comprises: an adhesive component selectedfrom the group of a cyanoacrylate adhesive, an anaerobic acrylicadhesive, and mixtures thereof, wherein the adhesive component comprisesa monomer of the formula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2-methoxyethyl group; and an electrically insulating filler; wherein theinstant setting adhesive composition has a thixotropic index from about4 to about
 6. 52. The method of claim 51 further comprising applying acatalyst to the lead fingers, die or the instant setting adhesivecomposition prior to the placing step.
 53. A method for applying anadhesive to a wafer comprising: providing a wafer having a surface; andapplying an instant setting adhesive composition onto a plurality ofportions of the surface of the wafer in a configuration, wherein theinstant setting adhesive composition comprises: an adhesive componentselected from the group of a cyanoacrylate adhesive, an anaerobicacrylic adhesive, and mixtures thereof, wherein the adhesive componentcomprises a monomer of the formula:

 wherein R is selected from the group of an alkaryl, a cycloalkenyl, anaralkyl, a 2-chlorobutyl group, a methallyl group, a crotyl group, and a2methoxyethyl group; and at least one additive selected from the groupof a thermal stabilizer, a thickener, a plasticizer, a toughener, aconductive filler, a dielectric additive, a moisture stabilizer, acuring inhibitor, an adhesion promoter, a storage stabilizer, acolorant, and an organic solvent; wherein the instant setting adhesivecomposition has a thixotropic index from about 4 to about 6, and whereinthe instant setting adhesive composition becomes non-flowable andsubstantially maintains the configuration in which the instant settingadhesive composition is applied within about 0.1 seconds to about 120seconds after the instant setting adhesive is applied to the surface.54. The method of claim 53 wherein the instant setting adhesivecomposition becomes non-flowable and substantially maintains theconfiguration within about 0.1 seconds to about 60 seconds.
 55. Themethod of claim 53 wherein the instant setting adhesive compositionbecomes non-flowable and substantially maintains the configurationwithin 0.1 seconds to 120 seconds at a temperature of about 20° C. toabout 30° C.
 56. The method of claim 53 wherein one or more zones of thesurface are essentially free of the instant setting adhesivecomposition, and further wherein the zones comprise singulation streets.57. The method of claim 53 wherein one or more zones of the surface areessentially free of the instant setting adhesive composition, andfurther wherein the zones comprise regions having exposed bond pads. 58.The method of claim 53 wherein applying the instant setting adhesivecomposition to the surface of the wafer comprises a technique selectedfrom the group of screen printing, depositing and patterning, syringeapplying, stenciling, dip coating, spraying, dot shooting, andcombinations thereof.